The miniaturized gas detectors of the prior art are such that water vapors or films cannot be tolerated on their active surfaces. As a result, heaters are incorporated in or used with the devices to keep the system dry. For example, L. Treitinger, P. Tischer and B. Schneider-Gmelch, in U.S. Pat. No. 4,338,281, issued July 6, 1982, show the use of highly doped silicon, doped until it is essentially metallic, to act as a resistance heater. Silicon dioxide is used to separate the silicon heater from the active metal oxide which may be, for example, SnO.sub.2 /PdO. Because of the intimate contact in the silicon heater and the active oxide (SnO.sub.2), low power consumption results. This low power consumption is, however, of the order of 0.1 watt per mm.sup.2 and is still higher than would be desirable.
As another example, M. Kimura, in U.S. Pat. No. 4,343,768, issued Aug. 10, 1982 sets forth a sensor heater design which provides relatively low power consumption. Silicon dioxide is used in the construction of the sensor in that a silicon dioxide film completely separates two conducting phases, namely the silicon phase and the platinum or palladium catalyst. The Kimura patent, like the Tretinger, et al patent, utilizes a heater structure so as to exclude both liquid water and water vapor. The power consumption is not specified but appears to be about the same as that in the Tretinger, et al structure. This is because both of the structures require heating which is significantly power consumptive.
A microdevice for gas and vapor sensing which would not require the use of a heater to exclude water and water vapor and which also was highly sensitive would provide a significant step forward over the background art just discussed.
The present invention is directed to overcoming one or more of the problems as set forth above.